A non-invasive procedure for assessing electrical activity in the heart will be evaluated. The procedure is an approach to the inverse problem of electrocardiography and incorporates a method of measuring torso transfer impedances directly on the patient at the time ECG data are collected. Transfer impedances are estimated from the measured voltages at the ECG leads produced by perturbing currents introduced sequentially at all electrodes on the torso surface during the quiet T-P interval. The proposed procedure will be designed and implemented in an electrolytic tank in the shape of a human torso containing lung and blood mass inhomogeneities. Validation of the procedure and error analysis will be performed on the chimpanzee.